The invention relates to a fixed carriageway for rail vehicles having sleepers embedded in a carriageway panel and a reinforcement, which comprises plural longitudinal rods and transverse rods disposed in the carriageway panel parallel and transverse to the sleepers.
The term “fixed carriageway” refers to a section of rail with a superstructure, in which the ballast is replaced by another material such as concrete or asphalt for example. In the construction of the fixed carriageway, the sleepers are adjusted and embedded in a casting compound, creating a carriageway panel. The substructure of the carriageway panel may comprise a hydraulically bonded support layer, a ballast support layer, a frost-protection layer, a foil or a geotextile.
In the operation of rail sections, it is necessary to determine whether a certain section of track is clear or whether a train is located thereon. To this end, track circuits can be used in which a transmitter feeds an audio frequency signal into the track in such a manner that the rails act as to-and-fro conductors. At a remote site, the signal is evaluated by a receiver and by means of the signal level received, it is decided whether the section of track between the transmitter and receiver is clear.
One of these track circuit systems, which is available under the reference UM71 and is used in various countries, operates with four carrier frequencies of between 1.7 and 3.1 kHz.
Due to the impedances of rails and track connectors, the signal levels of the track circuits are damped or energy is drained from the track circuits as the distance between transmitter and receiver increases. Since the system is impressed particularly by inductive voltage drops due to the frequencies used, this component of damping can be compensated by the regular arrangement of specified transverse capacitances between the two rails. On a clear section, with compensation, maximum track circuit lengths of 1500 meters can be achieved. In non-compensated realisations, on the other hand, only track circuit lengths of 450 meters maximum are possible. Conventional track circuit systems, such as the above-mentioned system UM71, have hitherto been used predominantly with ballast carriageways.
A reason for not using such track circuits in fixed carriageways, however, is the fact that in these carriageways transverse rods and longitudinal rods are present in the concrete support panel as reinforcement. In the reinforcing rods extending longitudinally to the track axis, due to the magnetic fields of the audio frequency rail currents, a voltage is induced. Closed short-circuit current paths can form via the transverse reinforcements. The losses thus occurring in the reinforcement rods cause additional damping of the track circuit signals or to additional energy depletion. A possible consequence of this is that the receiver of the track circuit no longer measures a sufficient level in spite of a clear section of track and thus signals that the track is occupied, which is not in fact the case.